JS.emscripten: adds connect callbacks to the ports. (#602)

This allows delaying the stack start until the asynchronous connections succeed.

src/utils/JSHubPort.cxx

@@ -34,7 +34,18 @@
 
 #ifdef __EMSCRIPTEN__
 
+#include <functional>
+
 extern int JSHubPort_debug_port_num;
 int JSHubPort_debug_port_num = 0;
 
+/// Invokes a function pointer.
+extern "C" void __attribute__((used)) invoke_fnp(std::function<void()> *fp)
+{
+    if (fp && *fp)
+    {
+        (*fp)();
+    }
+}
+
 #endif // __EMSCRIPTEN__

src/utils/JSSerialPort.hxx

@@ -46,8 +46,14 @@
 class JSSerialPort
 {
 public:
-    JSSerialPort(CanHubFlow *hflow, string device)
+    /// Constructor
+    /// @param hflow the CAN hub object in the local binary to add this port to.
+    /// @param device the serial device name (see list_ports output)
+    /// @param cb will be invoked when the connection succeeds
+    JSSerialPort(CanHubFlow *hflow, string device,
+        std::function<void()> cb = []() {})
         : canHub_(hflow)
+        , connectCallback_(std::move(cb))
     {
         string script = "Module.serial_device = '" + device + "';\n";
         emscripten_run_script(script.c_str());
@@ -96,9 +102,10 @@ public:
                         client_port.abandon();
                     });
                     c.on('data', function(data) { client_port.recv(data.toString()); });
+                    _invoke_fnp($1);
                 });
             },
-            (unsigned long)canHub_);
+            (unsigned long)canHub_, (unsigned long)&connectCallback_);
     }
 
     static void list_ports() {
@@ -119,6 +126,8 @@ public:
 
 private:
     CanHubFlow *canHub_;
+    /// This function will be invoked when the connection succeeds.
+    std::function<void()> connectCallback_;
 };
 
 #endif // __EMSCRIPTEN__

src/utils/JSTcpClient.hxx

@@ -47,11 +47,20 @@
 class JSTcpClient
 {
 public:
-    JSTcpClient(CanHubFlow *hflow, string host, int port)
+    /// Constructor
+    /// @param hflow the CAN hub object in the local binary to add this port to.
+    /// @param host the IP address or name of the remote host
+    /// @param port the TCP port number to connect to
+    /// @param cb will be invoked when the connection succeeds
+    JSTcpClient(
+        CanHubFlow *hflow, string host, int port,
+        std::function<void()> cb = []() {})
         : canHub_(hflow)
+        , connectCallback_(std::move(cb))
     {
         string script = "Module.remote_server = '" + host + "';\n";
         emscripten_run_script(script.c_str());
+
         EM_ASM_(
             {
                 var net = require('net');
@@ -73,13 +82,16 @@ public:
                         client_port.abandon();
                     });
                     c.on('data', function(data) { client_port.recv(data); });
+                    _invoke_fnp($2);
                 });
             },
-            port, (unsigned long)canHub_);
+            port, (unsigned long)canHub_, (unsigned long)&connectCallback_);
     }
 
 private:
     CanHubFlow *canHub_;
+    /// This function will be invoked when the connection succeeds.
+    std::function<void()> connectCallback_;
 };
 
 #endif // __EMSCRIPTEN__